Question about Aprilaire 550 Humidifier

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Transformer Hi I have had my transformer replaced three times since installing this 550 unit in 2004. Do you think it has something to do with the way the unit is hooked up to the furnace motor? My humidstat wall unit upstairs was working fine, giving me a reading all summer and fall , until i turned on the furnace and now the AprilAire doesn't work. I am unemployed and trying to fix this myself.....not sure I can.

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  • Anonymous Dec 16, 2008

    Educational, but doesn't solve the problem.
    I need to hire someone again and can't afford it. I was hoping someone would help walk me through the process. I'm not mechanically inclined and I"m not even sure if the water supply to the unit is on the right way.



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It sounds like a wiring problem. If you still have the instructions that came with the unit, look at the wiring diagram and make sure you have everything right. If you dont have the instructions, you can find them online. Be careful you dont zap yourself! When you're in there playing around with wires make sure you kill the power to the furnace at the breaker. Double check this with a voltage tester if you have one. Also, if you're not sure you may want to disconnect the unit until you can afford to have a qualified professional look at it or you may end up doing more harm than good.

Posted on Dec 16, 2008


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Before we replaced our furnace, I had to replace the transformer almost every year. When the new furnace was installed last year, the transformer disappeared. Now with winter coming on, the 550 hasn't

Hello, seems like there is no way to turn on the humidifier. There would either need to be a new transformer installed, a current sensing relay, or a sail switch to activate the humidifier when the blower motor kicks on.

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Hello, apply power directly from transformer to solenoid valve, it it does not turn on the solenoid valve must be replaced. If there is no voltage to the solenoid then follow the wires back and see where there is no voltage.

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Hello, yes the transformer will get a 120 volts from the Furnaces control board, there should be a terminal labeled HUM on the control board. You need to bring 2 wires one from HUM and one from a nuetral tap on the board to the line side of the transformer, this way every time the blower motor on the Furnace turns on the humidifier will aswell.

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1 Answer

I have no idea how to wire my Humidifier to the furnace! I am attempting to wire an Aprilaire Humidifier to an older furnace. The supplied wiring instructions are of no use to me because I have no terminal...

Hello, if the transformer you got with the humidifier is one that plugs into a receptacle than all you need is either a current sensing relay or sail switch. First connect one wire to transformer then connect to humidiistat then to either sail switch or current sensing relay and back to other terminal on transformer. if you use a sail switch then it will mount in the return air duct if you use a current sensing relay it will cradle the blower motors common wire. I will post a pic of both robhvac47_19.jpg current sensing relay

robhvac47_20.jpgSail switch

Feb 20, 2011 | Aprilaire 550 Humidifier

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I just installed a Honeywell HE 360 Humidifier I purchased at Home depot. I replaced a Aprilaire model 110 . I have a 120v power duplex that is hot with the furnace blower motor, on so I assumed the sail...

Hello, in order to turn your humidifier on with the furnace the 120 volts coming from your humidifer you must hook it up to a step down transformer, then the transformer will provide 24 volts to you humidistat and solenoid valve. So you need a wire from the HUM on your control board to transformer primary side and a wire from neutral on the board to primary side of transformer. Then you need low voltage wire from secondary side of transformer to humidistat from humidistat to humidifier.

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1 Answer

550 not working water supply is ok

Hello, check to see if you are getting 24 volts to the solenoid valve, if you are and it does not click on to let the water into the humidifier then the solenoid must be replaced. However if you are not getting 24 volts to the solenoid valve check if yuou are getting 24 volts at the transformer, if not then turn power off to transformer and check the continuity of the secondary side of the transfomer, you should have resistance if not replace the transformer. if that checks out good check the wire connection between transformer and solenoid and make sure it is tight. If wire connection looks good then either humidistat is bad or current sensing relay/sail switch.

Jan 30, 2011 | Aprilaire 550 Humidifier

1 Answer

I have a aprilaire 560, it stop working this year. (Dry skin) I checked the water supply to the solenoid it good, I repalce the solenoid 40/40 thinking that was the problem. Still not working, I check...

Hello, make sure you are getting 24 volts at the transformer, if not turn off power to transformer and check resistance on the secondary side of transformer, you should have resistance if not replace transformer. If you have 24 volts at transformer than check the wiring and make sure it is tight. the last thing to check is to make sure you are getting 24 volts in and out of the humidistat. if you are not replace humidistat.

Jan 29, 2011 | Aprilaire 550 Humidifier

1 Answer

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The first thing to check is if you are getting 24 volts at the transformer, if you are not then turn off power the transformer and check continuity. u should have continuity if not replace the transformer. If you are getting 24 volts at the transformer then apply 24 volts directly from transfomer to solenoid valve you should hear the solenoid cleck open and let the water in, if not then the solenoid is bad and must be replaced. If the solenoid does work by applying voltage directly to it then check the
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Jan 13, 2011 | Aprilaire 550 Humidifier

1 Answer

No water is coming from aprailaire 550

Hi check the jet inside could be blocked , filter could be blocked water tray full of scale needs cleaning ,check power to valve or transformer

Jan 23, 2010 | Aprilaire 550 Humidifier

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